Thermal analysis of coatings and substrate materials during a disruption in fusion reactors

In a tokamak fusion reactor, the frequency of occurrence and the severity of a plasma disruption event will determine the lifetime of the plasma facing components. Disruptions are plasma instabilities which result in rapid loss of confinement and termination of plasma current Intense energy fluxes to components like the rust wall and the divertor plate are expected during the disruptions. This high energy deposition in short times may cause severe surface erosion of these components resulting from melting and vaporization. Coatings and tile materials are proposed to protect and maintain the integrity of the underneath, structural materials from both erosion losses as well as from high thermal stresses encountered during a disruption. The coating thickness should be large enough to withstand both erosion losses and to reduce the temperature rise in the substrate structural material. The coating thickness should be minimized to enhance the structural integrity, to reduce potential problems from radioactivity, and to minimize materials cost. Tile materials such as graphite and coating materials such as beryllium and tungsten on structural materials like copper, steel, and vanadium are analyzed and compared as potential diverter and first wall design options. The effect of the sprayed coating properties during the disruption is investigated. Porous sprayed material may be found to protect the structure better than condensed phase properties. The minimum coating thickness required to protect the structural material during disruption is discussed. The impact of self shielding effect by the eroded material oil the response of both the type/coating and the substrate is discussed